Ionospheric irregularities are an important phenomenon in scientific studies and applications of radio-wave propagation. Spread-F echoes in ionograms are a type of high-frequency band irregularities that include frequency spread-F (FSF), range spread-F (RSF), and mixed spread-F (MSF) events. In this study, we obtained spread-F data from four ionosondes at low- and mid-latitudes near the 120°E chain in China during the 23rd solar cycle. We used these data to investigate spread-F occurrence percentages and variations with local time, season, latitude, and solar activity. The four ionosondes were located at Haikou (HK) (20°N, 110.34°E), Guangzhou (GZ) (23.14°N, 113.36°E), Beijing (BJ) (40.11°N, 116.28°E), and Changchun (CC) (43.84°N, 125.28°E). We also present possible correlations between spread-Fs and other ionospheric parameters, such as the critical frequency of the F2-layer (foF2) and the virtual height of the bottom-side F-layer (h′F). In particular, we investigated the possible threshold of the foF2 affecting the FSF and the relationship between the h′F and the RSF. The main conclusions are as follows: (a) the FSF occurrence percentages were anti-correlated with solar activity at all four sites; meanwhile, RSF occurrence rates increased with the increase in solar activity at HK, but not at the other three sites; (b) FSF occurrence rates were larger at the mid-latitudes than expected, while FSFs occurred more often after midnight; (c) the highest FSF occurrence rates mostly appeared during the summer months, while RSFs occurred mostly in the equinoctial months of 2000–2002 at HK and GZ; (d) a lower foF2 was suitable for FSF events; nevertheless, h′F and RSF occurrences satisfied the parabolic relationship; (e) the foF2 thresholds for FSFs were 15, 14, 7.6, and 7.8 MHz at HK, GZ, BJ, and CC, respectively. The h′Fs occurring between 240 and 290 km were more favorable for RSF occurrences. These results are important for understanding ionospheric irregularity variations in eastern Asia and for improving space weather modeling and forecasting capabilities .

The propagation of electromagnetic waves in the troposphere is significantly influenced by atmospheric refractivity and atmospheric ducts. Thus, abundant statistics on atmospheric refractivity and ducts are essential for reliable propagation prediction. In this study, we develop novel digital maps of atmospheric refractivity and atmospheric ducts based on the processing of radiosonde observation (RAOB) data and surface observation (SUOB) data collected from 2005 to 2014, including wet term of surface refractivity, refractivity gradients, and atmospheric ducts. The new digital maps, referred to as RADIO maps are defined as RADIOS and RADIOS2 maps. The RADIOS maps, which are world maps of refractivity gradients and atmospheric ducts, are obtained from data collected at radiosonde stations at 892 sites. The RADIOS2 map, which is a world map of the wet term of surface refractivity, is obtained from data collected at radiosonde and surface stations at 3218 sites. To test the consistency between RADIO maps and ITU-R ERAI (International Telecommunication Union Recommendations employing ERA-Interim (European Centre for Medium-Range Weather Forecasts Re-Analysis-interim) reanalysis data for 36 years from 1979 to 2014) maps; a comparison is performed with the cumulative distributions of refractivity gradients at two radiosonde stations. The accuracy of RADIO maps is checked through comparisons with the maximum, mean, and standard deviation of the relative errors, which are obtained from observed values and predicted values, between RADIO maps and ITU-R ERAI maps. Our results show that: 1) RADIOS2 map is consistent with the current ITU-R ERAI map with respect to the wet term of surface refractivity; 2) $\Delta N_{65\,\mathrm {m}}$ (50) and $\beta $ obtained from RADIOS maps are larger than those obtained from ITU-R ERAI maps in low-latitude coastal and marine areas; and 3) comparisons between RADIOS and ITU-R radios_duct maps (i.e., the world digital maps obtained from a 20-year (1977–1996) dataset of 661 radiosonde stations released by ITU-R P.453-14) show that ITU-R radios_duct maps predict lower occurrences of surface and elevated ducts at low latitudes. Overall, this study demonstrated that the new maps based on observations over the past ten years provide more accurate and reliable information than other traditional maps in terms of atmospheric refractivity, refractivity gradients, and atmospheric ducts.

In some frequency-sharing studies between fixed service and space radiocommunication services, including fixed-satellite, broadcasting-satellite, and space science services, it is necessary to estimate the apparent elevation angle of a space station, taking into account the atmospheric refraction. Recommendations ITU-R (International Telecommunication Union—Radiocommunication) P.834-9 and F.1333-1 detail similar methods regarding calculating the refraction correction for the elevation angle of the mean annual global reference atmosphere. Herein, both methods are approximated using the bending angle from the ground to the infinity height; this approach is most suitable for geosynchronous orbit satellites. In this paper, new methods for calculating the refraction correction for the elevation angle are proposed regarding the mean annual global reference atmosphere given in Recommendation ITU-R P.835-6. Specifically, the results of the ray-tracing method are fitted. The height of the new formulae is 100 km above sea level. For higher altitudes, correction methods are given based on free-space propagation. The proposed methods can be applied to the calculation of the refraction correction for the elevation of the mean annual global reference atmosphere for satellites at different orbital heights. Furthermore, these new methods compare favourably to the two ITU-R Recommendations.

In this article, we study the optical force exerted on nanorods. In recent years, the capture of micro-nanoparticles has been a frontier topic in optics. A Photonic Jet (PJ) is an emerging subwavelength beam with excellent application prospects. This paper studies the optical force exerted by photonic jets generated by a plane wave illuminating a Generalized Luneburg Lens (GLLs) on nanorods. In the framework of the dipole approximation, the optical force on the nanorods is studied. The electric field of the photonic jet is calculated by the open-source software package DDSCAT developed based on the Discrete Dipole Approximation (DDA). In this paper, the effects of the nanorods’ orientation and dielectric constant on the transverse force F_x and longitudinal force F_y are analyzed. Numerical results show that the maximum value of the positive force and the negative force are equal and appear alternately at the position of the photonic jet. Therefore, to capture anisotropic nanoscale-geometries (nanorods), it is necessary to adjust the position of GLLs continuously. It is worth emphasizing that manipulations with nanorods will make it possible to create new materials at the nanoscale.

The multiple-input multiple-output (MIMO) phase of the received signal is the most important parameter in the line-of-sight MIMO (LOS MIMO) system. The MIMO phase turbulence often occurs in practical applications, and the LOS MIMO system cannot operate normally in severe cases. However, there is no practical MIMO phase prediction method presently. A tropospheric radio-duct during phase turbulence was observed using a mesoscale numerical weather prediction (NWP) model. In this study, a novel MIMO phase prediction method was proposed. In the method, the tropospheric refractivity profile was predicted using a mesoscale NWP model, and then MIMO phase was predicted by the parabolic equation model. The comparison of the predicted MIMO phases with the measured results shows good agreement. MIMO Phase turbulence prediction method can provide support for LOS MIMO system performance prediction.

Rain height is crucial for rain attenuation prediction along slant paths, such as Earth-space links. The global digital map of the mean annual rain height is given in Recommendation ITU-R P.839-4. The disadvantage of this model is that heavy rainfall in most regions of the middle and high latitudes of the world is typically concentrated over a few months, such as summer in North China, and the mean rain height during these months and the mean annual rain height are often significantly different. In this study, a new weighted mean annual rain height is proposed by using the ratio of the mean monthly rainfall to the mean annual rainfall as the weight. The analysis shows that the weighted mean annual rain heights have been closer to the statistical rain heights during heavy rainfall in general. On the other hand, the work of this paper helps to improve the accuracy of the rain attenuation prediction model on Earth-space links in China. However, the weighted mean annual rain heights have different characteristics for different rainfall climate zones. This study will contribute to the research of rain attenuation modelling on Earth-space links.